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©KAUST 2023; Eliza Mkhitaryan

The sweet smell of successful wastewater treatment

The use of engineered algae to deliver clean water and valuable co-products from treated wastewater opens new opportunities for water treatment.

An engineered alga (Chlamydomonas reinhardtii) has been grown directly in treated wastewater effluent to produce a valuable co-product. This work by a KAUST team led by Kyle Lauersen in collaboration with KAUST environmental scientist Peiying Hong is the first of its kind to show that the algae used in genetic engineering studies could also have real-world translation in direct production-relevant conditions.

Conventional aerobic and chemical wastewater nutrient-removal methods use a lot of energy, have long process times and produce both carbon emissions as well as excess sludge discharge.

From left: Kyle Lauersen, Bárbara de Freitas and Sebastian Overmans in collaboration with KAUST environmental scientist Peiying Hong (not in the photo), have successfully grown an engineered algae in treated wastewater effluent. The algae can consume nitrogen and phosphorus from the wastewater to produce valuable co-products, such as the fragrant compound patchoulol. ©KAUST 2023; Eliza Mkhitaryan

“Anaerobic membrane bioreactors (AnMBRs) require less energy and produce at least ten times less sludge, while efficiently removing organic matter and suspended solids,” says Hong, whose research focuses on solving water scarcity in arid regions by developing high-quality, treated wastewater as an alternative water resource.

For the past 18 months, Hong and her team have run a demonstration-scale AnMBR-based wastewater treatment plant in Jeddah — a joint initiative between KAUST and the Saudi Authority for Industrial Cities and Technology Zones (MODON). Using technology developed by Hong, the plant treats 25,000 to 50,000 liters of wastewater per day.

The outputs from AnMBR — methane and carbon dioxide gas plus water containing ammonium and phosphate — can be used to grow algae, which uses up CO2 as well as nitrogen and phosphate from the effluent to feed algal biomass.

Lauersen and other researchers have previously shown that engineered algae can be used to produce natural molecules, such as the sesquiterpene patchoulol (the fragrant compound in patchouli oil). These molecules are harvested from the growing algae using a biocompatible solvent, a process known as “microbial milking,” developed by Lauersen and his team.

©KAUST 2023; Eliza Mkhitaryan

In Lauersen’s algal biotechnology lab at KAUST, postdocs Bárbara de Freitas and Sebastian Overmans investigated the performance of highly domesticated patchoulol-producing C. reinhardtii strains directly in effluent from an anaerobic membrane bioreactor running in Hong’s lab.

“We had previously explored the use of wild-type algal strains as a polishing step for the treated wastewater after AnMBR but did not get bioproducts at a scale that would make economic sense,” says Hong.

“Collaborating with Kyle’s team to get a higher value-added bioproduct from a genetically modified strain enabled us to address this challenge.”

In different concentrations of raw effluent, the algae completely consumed nitrogen and phosphorus. It grew in all dilutions of effluent in water, including 100 percent (raw effluent) and 50 percent dilutions.

“We were able to simultaneously generate clean water, algal biomass and convert waste CO2 into the valuable patchoulol co-product,” says Lauersen.

He believes the milking of co-products during nutrient removal could be a promising way to get value from lost resources in wastewater.

“The demonstration that domesticated and engineerable algae can grow directly in AnMBR effluent and yield high-value side products drastically expands the range of possibilities to increase the circular value of these systems,” he says.

As urban populations grow, including in Saudi Arabia, effective wastewater treatment strategies are required that are compatible with the local environment.

Using photobioreactor-simulated conditions based on the weather around Saudi Red Sea shores, the algal cultures thrived in AnMBR effluent, producing high levels of biomass even in hot summer temperatures.

Lauersen says such environmental modeling using local weather data in replicate bioreactors will be a valuable tool for benchmarking the performance of different algal strains at various locations.

Hong believes Saudi Arabia and the region have the right conditions to scale up the use of algae for wastewater treatment.

“It would be a suitable method for further purifying treated wastewater, in turn maximizing the recovery of resources from the waste stream,” she concludes.

 “Algal culture seems well suited for pairing with wastewater treatment, especially from AnMBRs,” says Lauersen.

He believes the process could be extended to other high-value molecules, such as taxadiene, the precursor for the anticancer drug Taxol, produced by engineered algae.

The researchers are continuing to engineer new molecules of value and trying to produce higher volumes of these co-products from the algae.